Credit: Greg Stewart/SLAC National Accelerator Laboratory
In this illustration, a near-infrared laser beam hits a piece of ordinary glass and triggers a process called high harmonic generation. It produces laser light pulses (top right) that are just billionths of a billionth of a second, or attoseconds, long, and the photons in those pulses are much higher energy than those in the original beam. The insets zoom in on how this happens. When the incoming laser light knocks electrons (e-) out of atoms in the glass, they fly away, loop back and reconnect with either their home atom (lower right) or a neighboring atom (upper left). These reconnections generate bright bursts of light, forming a “train” of attosecond pulses that leaves the glass and can be used to probe electron movements in solids.